Most people dread needles. The sight alone of a large needle is enough to cause many patients to become anxious and tense. This reaction in turn may cause the patient's muscles to become tight and hard, making needle penetration even more difficult and painful.
Many medications must be injected intramuscularly with a substantially large needle necessary to penetrate the muscle layers and transfer more viscous medications through the needle. These types of injections are painful, because the long needle penetrates deeply through the layers of skin as well as many layers of muscles.
Intramuscular injections involve injecting a medication into the muscle layers. To avoid injecting the medication intravascularly, an extra step is taken by aspirating the syringe after the needle is inserted but prior to depressing the plunger. If blood is drawn up into the syringe, then the tip of the needle has entered a blood vessel, and the needle must be repositioned in order to clear the vessel. Some health care workers may forget or skip this step, which may cause adverse effects when the medication is injected intravascularly.
Accordingly, it has become desirable to provide an injection device that first injects a numbing agent at the site of injection with a fine gauge needle, and then inserts the larger medication needle through the anesthetized skin painlessly and then injects the medication intramuscularly at the desired depth. The numbing of the skin is almost immediate.
In one aspect of the invention, a painless injection apparatus includes a first injector having a first storage chamber storing a numbing agent, a first needle, and a first plunger, and a second injector having a second storage chamber storing a medication, a second needle, and a second plunger. The injection apparatus further includes a plunger actuation device coupled to the first and second plungers and the second storage chamber. The plunger actuation device is adapted to sequentially advance the first plunger, the second storage chamber, and then the second plunger to inject the numbing agent and then the medication painlessly through the skin.
In another aspect of the invention, a method for painless injections includes the steps of inserting a first fine gauge needle of a first injector into a patient's skin, and actuating a first plunger of the first injector to inject a numbing agent into the patient's skin. Thereafter, a second plunger is actuated to advance and insert a second needle of a second injector positioned in close proximity to the first injector and forming an integral unit therewith through the patient's anesthetized skin to a desired depth. A third plunger of the second injector is then actuated to retract the medication plunger a predetermined amount to aspirate for blood. If blood is not detected, the third plunger of the second injector is actuated to inject a medication to the desired depth in the patient's tissues.
Another aspect of the device is that it could be adjusted to insert the medication needle to varying depths to allow for varying thicknesses of muscle and/or subcutaneous tissue or fat.
A technical advantage of the invention includes the availability of an essentially painless intramuscular or subcutaneous injection with the convenience of one integrated injection device. Additionally, with the use of pre-filled and pre-labeled medication cartridges, the incidence of dosage errors is greatly reduced, and wrong medication accidents would be less likely. With automatic aspiration, the occurrence of injecting a medication intravascularly when an intramuscular injection is intended is eliminated. A further technical advantage includes the lessening of the patient's anxiety and muscle tightening at the sight of a large needle because the device does not look like a "shot" and the medication needle is not visible. Another advantage of the device is that it could be adjusted to insert the medication needle to varying depths to allow for varying thickness of muscle and/or subcutaneous tissue or fat. An additional advantage of the injection device provides for an automatic retraction of the needles into the housing, so that accidental and inadvertent needle stick is essentially eliminated to avoid the transmission of contagious diseases. Further, because there is no exposed needles, safe disposal of used cartridges is also possible.